There is a well-known valve stopping device that can stop either an intake valve or an exhaust valve of an internal combustion engine in a closed state. The valve stopping device includes an actuator for stopping a valve and a control device for controlling the actuator. Various mechanical schemes or electrical schemes were proposed for the actuator included in the valve stopping device. However, the actuator is generally configured so that an electrical signal input from the control device is used to control an actuator operation for stopping a valve or making it operative. A device disclosed, for instance, in JP-A-2001-317318 stops a valve or makes it operative by allowing an electrically-driven solenoid to manipulate a coupling pin and change the coupled state of a rocker arm that is divided into a plurality of segments.
When the valve stopping device stops a valve in the closed state, a cylinder provided with the valve comes to a halt. When the valve stopping device is incorporated in an internal combustion engine having a plurality of cylinders, it can make all the cylinders operative or some of the cylinders operative by controlling a valve stopping device operation in such a manner as to stop valves or make them operative on an individual cylinder basis or on an individual cylinder group basis. As fuel efficiency is improved by changing the number of operative cylinders in accordance with load and engine speed, great benefits are achieved when the valve stopping device is incorporated in the internal combustion engine.
However, when the valve stopping device is to be incorporated in the internal combustion engine, consideration should be given to failure of the valve stopping device. If the valve stopping device becomes faulty for some reason, the valves cannot be stopped, cannot be made operative, or may be erroneously stopped. The valve stopping device may become faulty due to either the failure of an individual actuator or the failure of the control device. However, a more serious consequence occurs when the control device becomes faulty. When the control device is faulty, an electrical signal to be output to the actuator for each cylinder may stay on or stay off. In such an instance, the valves for all cylinders may be erroneously stopped to bring the entire internal combustion engine to a stop. If a signal to be output to the solenoid of the device disclosed, for instance, in JP-A-2001-317318 stays on due to a fault in the control device, the valves for all cylinders are stopped to make the internal combustion engine inoperative. When the internal combustion engine is inoperative, it is obvious that a vehicle using the internal combustion engine as its power unit is unable to run.